Abstract Few studies have been designed to assess impacts of prenatal pesticide exposures on adverse pregnancy events and outcomes including preterm birth and fetal growth. Earlier epidemiological studies were mainly relatively small case/control studies, with limited information about exposure relying on self-reported data that produced equivocal findings. Recently, reports emerged suggesting pregnancy complications such as gestational diabetes, or preeclampsia in relation to early pregnancy exposure to pesticides. Endocrine disrupting properties suggested for several classes of agricultural pesticides, have been proposed to contribute to increases in risks for adverse pregnancy events and birth outcomes. Thus a well-designed large scale population based study with detailed and reliable pesticide exposure assessment (not based on parental recall) is urgently needed. Our proposed study will address this gap in a highly efficient and timely manner, leveraging our existing resources established with funding from NIH, by combining sophisticated pesticide exposure assessment with large-scale population and record-based birth cohort data. California is an excellent locale for such a study: the state ranks 1st among US states in agricultural production, with 1/4 of US total agricultural pesticide use, and is the only state which maintains a statewide pesticide use reporting system. Building onto this unique resource, our team has longstanding experience developing and applying a geographic pesticide exposure assessment tool (GRAPES) that utilizes the unique California Pesticide Use Report system, in combination with agricultural land-use maps, to derive estimates of residential exposures to specific pesticides. We propose to conduct a records and population based study focused on the agricultural counties of California, including the Central Valley, one of the world?s most intensely farmed regions (the Nation?s ?Fruit Basket?), using all births 1998-2013 (n>700,000) for which we will newly create detailed periconceptional/ prenatal and trimester specific pesticide exposure estimates. We will comprehensively assess risks for preterm birth, fetal growth indicators, fetal and infant death, and pregnancy complications (gestational diabetes, preeclampsia). This approach will provide the - to our knowledge - largest population based study with advanced exposure assessment not relying on self-report, to address the hypotheses that exposure to specific chemicals such as endocrine disrupting agents increase risk for adverse birth outcomes. For this study, we will focus on chemicals used in high volume, potential endocrine disrupters, and those previously found to have adverse effects in animal/human studies, including glyphosate, organophosphates, neonicotinoids, pyrethroids. Thus, leveraging the resources we previously created with NIH funding, this study will likely have high impact as it addresses public concerns about prenatal health effect of pesticide exposures, and has the potential to influence public health policies and future research in a highly cost-efficient manner. The design of future biomarker studies we plan, will build upon the findings of the proposed record-only study.